Adds the following new Zuul job for testing deployment of Monasca and
associated services:

* kolla-ansible-centos8-source-monasca

All core OpenStack services except for Keystone are disabled to ensure
enough memory is available.

A follow up patch will replace the basic tests here with Tempest.

Co-Authored-By: Doug Szumski <doug@stackhpc.com>

Change-Id: I5d33fd3d7b69798ba0aa23509f7b809065f61c19